I already get quite amazing battery life from my Treo 650, and have a spare 1800 mAh battery that I carry on trips. I saw that Seidio now has a 2400 mAh battery that fits into the same compartment as your standard battery, yet adds a bit more weight.

The battery sells for only US$39.95, works in both the Treo 650 and new Treo 700w, and reportedly adds 33% more standby and talk time over the standard battery. This is great news for those who rely on the Treo as their primary device.